Tuesday, 12 May 2015

Low cost laser cut optical mounts

I have been thinking about low cost ways of mounting optics in the lab and as long as you don't need a very rigid mount (i.e. for interferometer) you can get away with these plastic optical mounts.

The advantages of these laser cut mounts over 3d printed mounts are the speed at which you can make a mounts which is an order of magnitude faster and the cost (if you wanted to outsource making of them) is much lower with many different companies now providing low cost laser cutting. We have a CO2 laser cutter in the lab so we can make around ten of these in about 10-20 minutes. They are designed for 1 inch 25.4 mm optics such as lenses and mirrors and with the springs allow for adjustment and alignment of the optics.

A screw in the side holds the optic in place while the three bolts offset from the mounting plate allow for adjustment of the angle of the optic.

The back mounting plate has a slot for a 4 mm bolt to connect it to an optical post.

One big improvement would be to cut the same design out aluminium which would allow for a more rigid design so that more precise instruments could be constructed. Comparing the physical properties of different materials.

Material Coefficient of linear expansion (μm/(m K)) Young's Modulus (MPa)
Acrylic 75 3200
Aluminium 22.2 69000
PET 59.4 2700
PLA 80-90 1750
ABS 80 2200
Sources 1,2,3,4,5

Aluminum is optimal with a very high rigidity and low thermal coefficient of linear expansion. PET has a low coefficient but isn't as rigid as Acrylic. PLA and ABS both 3d printed materials lack rigidity and have high thermal coefficients. So for some applications acrylic optical mounts may provide high enough rigidity with low enough thermal expansion for some applications. However I can imagine some crosslinked epoxies could improve the properties of optical mounts made by 3d printers (quick search found a resin with Young's modulus of 2700)

I am currently working on using these in a spectrometer design. I will upload the designs soon for the optical mount and fixtures needed once I have refined the design a bit more.